1. Field of the Invention
This invention relates generally to a color television camera and is more particularly directed to a color television camera with an improved automatic gain control (AGC) system.
2. Description of the Prior Art
In the art there has been proposed a color television camera using one image pickup tube in which an AGC system is provided to produce a video signal with a constant level even if the amount or intensity of incident light to the camera is changed.
By way of example, with one of the prior art systems, the bias voltage for the target of its image pickup tube is changed in accordance with the level of a produced luminance signal to make an output voltage from the image pickup tube constant.
With another one of the prior art systems, the target voltage of its image pickup tube is made constant and an AGC circuit is provided at the output side of the image pickup tube which is controlled in accordance with the level of a produced luminance signal.
Accordingly to the prior art systems, the level of a luminance signal contained in the camera output is held substantially constant regardless of the amount or intensity of incident light. However, since in the prior art the AGC system operates for both of luminance and chrominance signals, if an object of, for example, red color is photographed by the camera in a dark place, the luminance signal is increased to a predetermined level by the AGC system, but the level of a red color signal is also increased. Thus, a video signal in which a red color is emphasized excessively is produced. As a result, an unnatural picture is reproduced.